{"id":5609,"date":"2020-01-13T22:43:54","date_gmt":"2020-01-13T22:43:54","guid":{"rendered":"https:\/\/course.oeru.org\/eths101\/?page_id=5609"},"modified":"2020-01-13T22:43:54","modified_gmt":"2020-01-13T22:43:54","slug":"relative-and-absolute-ages","status":"publish","type":"page","link":"https:\/\/course.oeru.org\/eths101\/learning-pathways\/rock-record\/relative-and-absolute-ages\/","title":{"rendered":"Relative and Absolute Ages"},"content":{"rendered":"
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Fossils are not only interesting, intriguing and beautiful, they can also be very useful<\/b>\n<\/p>\n

Using the fossil succession spatially<\/span><\/h2>\n
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Canals were dug all over Europe and England in the 1700s to transport large volumes of raw materials and goods required for the new Industrial Revolution. In England, William Smith was building canals.<\/p>\n

\nHe realised that some strata were easier to dig than others. He noted that the strata contained fossils and that the fossils succeeded each other in a systematic way.\n<\/p>\n

\nUsing these ideas he could predict the location of strata and plan his canal routes to be the most cost effective. He made the first geological map, published in 1815.
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Using fossil succession across time (temporally)<\/span><\/h2>\n
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In the early to middle 1800s people began to divide rocks and fossils into different groups and understand their relationship to one another in relative time. Fossils were divided into the Paleozoic era (Palaeozoic = old life), Mesozoic era (=middle life) and Caenozoic era (Cenozoic = young life)<\/b>.<\/p>\n

John Phillips (the nephew of William Smith) drew the elegant to show the abundance of fossils through time.\n<\/p>\n

The curve illustrates the point that Greg made in his lecture on fossils: that as you go back in time there are fewer fossils. In this curve, you also see that there are two necks or times when there are very few fossils between the main eras. These breaks coincide with mass extinctions.\n<\/p>\n

In a relative sense, fossils can provide information on biozones in the rocks or biostratigraphy<\/b>.\n<\/p>\n

To be useful for relative dating, fossils must be common and widespread. Pollen, that Greg mentioned in his video are excellent biozone fossils. Individual fossil species that only lived for a short duration can be useful as index fossils. More often it is a group of fossils, called a fossil assemblage, used together that provide a better constraint on the relative ages of rocks. Here is a diagram on how this works:\n<\/p>\n

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Biozones<\/div>\n<\/div>\n<\/div>\n


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